In flow regulators, an expandable, resilient inner plug swells or expands within a closed housing to constrict the flow of a fluid past the regulator. Ordinarily, the fluid is natural gas. The resilient inner plug is normally expanded to constrict flow, the expansion being accomplished by squeezing the two ends of a resilient plug with a hydraulic control system, whereupon the resilient plug is shortened in length, swells in diameter and constricts the annular flow space on the interior of a metal housing. The inner plug is exposed to damage by particle impingement from the flowing gas. It is also subject to damage by taking a compression set. This is accomplished dependent on a number of scale factors and is cumulative with time. Such plugs are constructed of more or less uniform diameter along the length of the plug. Nevertheless, damage is not uniformly distributed. At first blush, one would imagine that compression set, in the plug, is maximum at the center of the plug and reduced at the ends. The flowing gas seems to move the bulge accomplished on permanent compression set towards the downstream end. Usually a permanent compression set bulge damages the inner plug at the point of maximum bulge protrusion where a minimum radius occurs, and plug failure is normally manifested by breaking of pieces of the plug at this stress intensified region. Typically it will occur around the plug but its lengthwise location is normally found at the minimum radius, maximum bulge location defied above.
Reinforcing materials have been placed heretofore in resilient plugs. However, the reinforcing which is taught in this disclosure is believed to provide a new, useful and unobvious construction. It is a plug construction characterized by end caps which lap over the end of the plug to provide metallic and hence stable support and dimensional control. So to speak, the plug cannot bend, flex or bulge in that region. The end caps cooperate with multiple plies of reinforcing material near the outer surface. The reinforcing must be within the body to lend its strength to the body. If it is too deep within the body, the layer on the exterior will readily peal away. The reinforcing is preferably located just below the surface. Equally important, the reinforcing ply is formed of lengthwise fibers which do not elongate. They are molded into the body and, therefore, do not stretch, providing strength to the body. The fibers are folded under at the ends. This positions them in a bonded relationship beneath the end caps and held to the body by bonding. Moreover, the fibers, while stretching in the lateral dimension, do not elongate and control the bulging of the resilient body and prevent the formation of a damaging bulge. The reinforced fibers found in multiple plies protect the regions of stress concentration and compression set, thereby extending the life of the plug. The life can be extended quite successfully with the incorporation of two plies. While an additional number can be added, two plies are believed to be the optimum result. They provide sufficient strength to the plug. Three or more plies are permissible but there is a point of diminishing returns, and also they tend to, depending on the hardness of the rubber and the gauge of the fibers in the plies, strengthen the plug to the point of hardness wherein there is too little resiliency and excessive hydraulic pressures are required to operate the plug.
With the foregoing in view, this disclosure is summarized as a resilient plug construction incorporating reinforcing plies. The reinforcing plies are constructed of fibers which are nonyieldable in one dimension and the fibers are placed so that the length of the fibers protects against bulging. The fibers in a ply are joined in a resilient sheath, and the ply is able to stretch in the transverse dimension. The fibers which collectively form each ply are, therefore, able to expand as the diameter increases during compression. The inner valve is also constructed with stress rings at the end, the stress rings comprising end plates bonded to the resilient plug or body and having concentric, overlapping rings at the ends to thereby clamp the rings to the body. The threads which form the ply are lapped under at the stress rings.